Modulation drive circuit for CRT deflection of television and data display termials

Abstract

An LC tank circuit in the collector of a power transistor controls the vertical modulation of the horizontal deflection of a CRT through additional deflection coils properly oriented. The tank circuit is tuned at a frequency nf for the desired modulation, where n is the number of cycles of oscillation of the tank for each drive pulse at a frequency (pulses per second) f, and each drive pulse is adjusted in width to one fourth or less of a cycle of the modulation frequency nf using an adjustable RC differentiating circuit and a threshold device to couple a squarewave signal at frequency f to the base of the power transistor.

What is claimed is: 
     
       1. In a cathode ray tube for a television receiver or monitor, or a data display terminal, which scans horizontal rasters with predetermined space between rasters for the display of video or data signals, means for vertical modulation of the rasters by additional deflection coils positioned on the neck of the cathode ray tube and oriented for vertical deflection while deflection coils in a yoke of the cathode ray tube are driven by horizontal and vertical deflection signals comprising a signal source at a frequency f,   a power transistor having a resistor connected between the emitter thereof and a source of power, and the additional deflection coils connected in series between circuit ground and the collector of said transistor:   a capacitor coupling said additional deflection coils to the collector of said transistor,   an LC tank circuit connected between the collector of said power transistor and circuit ground, said L tank circuit being tuned to a frequency nf, where n is a small integer orders of magnitude smaller than f, and   means responsive to said signal at frequency f for turning on said power transistor for less than one fourth of a modulation cycle at said frequency nf.   
     
     
       2. The combination defined in claim 1 for a data display terminal wherein said signal at frequency f is a squarewave signal derived from a clock pulse train at a frequency nf. 
     
     
       3. The combination as defined in claim 2 including means for dividing said clock pulse train at a frequency nf by n to obtain a frequency signal at frequency f, and   means for adjusting the phase of said signal at frequency f.   
     
     
       4. The combination as defined in claim 3 wherein said phase adjusting means includes an adjustable LC tank circuit for phase adjustment. 
     
     
       5. The combination of claim 4 including an RC differentiating circuit for adjustment of the period said power transistor is turned on during each cycle of said signal at frequency f, and a threshold device for coupling said RC differentiating circuit to the base of said power transistor, whereby an adjustment of the RC time constant of said differentiating circuit will adjust the period said power transistor is turned on for each cycle of said signal of frequency f.